With color photographic light-sensitive materials based on the subtractive color process, various investigations have been made for the purpose of improvement in sharpness, improvement in graininess, improvement in color reproducibility, or increase of sensitivity.
Couplers which release a photographically useful group are one technique for accomplishing such purposes. Recently, in addition to couplers which release a photographically useful group from the coupling position thereof, couplers which release a photographically useful group through a timing group have been disclosed. Such couplers are disclosed, for example, in U.S. Pat. Nos. 4,248,962 and 4,409,323, etc. Further, another attempt wherein couplers which release a coupler capable of releasing a photographically useful group are utilized has been made as described in U.S. Pat. No. 4,438,193, etc.
In Japanese Patent Application (OPI) No. 138636/82 (the term "OPI" as used herein means an "unexamined published patent application"), there are disclosed examples of couplers capable of releasing an ED (electron donating) compound (a reducing agent). More specifically, the couplers described in Japanese Patent Application (OPI) No. 138636/82 can be represented by the formula EQU COUP--ED
wherein COUP represents a photographic coupler residue capable of forming a dye image upon a reaction with the oxidation product of a color developing agent; and ED represents a group which is bonded to COUP at the coupling position of COUP and which is cleaved from COUP and is capable of undergoing an oxidation reduction reaction with the oxidation product of a color developing agent.
These compounds are, however, completely different from the compounds according to the present invention, since they are used only for the purpose of reducing the oxidation product of a developing agent. On the contrary, it is necessary that the compounds according to the present invention release a photographically useful group.
Although these known couplers exhibit improvement to some extent, it is not totally satisfactory, and further improvement has been desired.